Prior art teaches such a method and device. Radiation backscattered by the dispersed medium in the form of a light flux traverses the separating wall between the dispersed medium and the receiver of the light flux backscattered by said dispersed medium, before reaching said receiver; and as a result, the applicant has confirmed that said wall reflects a part of the light rays backscattered by the dispersed medium, and sends them back into the latter, these reflected rays being able then to be backscattered once again by the medium in the direction of the wall and being able to reach the receiver of the light flux located on the other side of this wall, inducing perturbations of the light flux backscattered by the dispersed medium with respect to the emitted light flux, and as a result, measurement errors of the light flux backscattered by the dispersed medium. In fact, the analysed dispersed medium is in general of a higher optical index than that of air and lower than that of the material forming the wall. Furthermore, the light rays reemitted by the medium can demonstrate very inclined exit angles. Calculation models using the measurement of the backscattered light flux do not take into account those light rays reemitted by the medium.
FIG. 1 illustrates the problem of light rays reflected by the wall and reemitted by the medium. The medium 1 comprises for example particles 2 on which the light rays are diffused; certain rays 4 backscattered by the medium traverse the wall 3 in order to form the backscattered light flux which is to be measured, whilst other backscattered light rays 5, instead of traversing the wall 3, are reflected by the latter and sent back into the medium 1 which can reemit them at another position so that they are added to the backscattered light flux, therefore perturbing in particular its distribution. The reference 6 illustrates the backscattering spot which forms the backscattered light flux. FIG. 2 shows a distribution 7 in fine lines, which is radial according to the radius ρ of the light flux F in the backscattering spot, in which the perturbation 8 caused by the light rays reemitted by the medium is presented in thick lines. It is confirmed that this perturbation 8 is not negligible taking into account its large amplitude.